1. Field of the Invention
The present invention relates to a plunger pump and, more particularly, to a plunger pump which may be employed as a jet scrubber in semiconductor manufacturing equipment.
2. Prior Art
Plunger pumps are arranged to pressurize a liquid drawn in through a suction opening and discharge it from a discharge opening under high pressure. FIGS. 4 and 5 show the internal structure of a conventional plunger pump. As illustrated, a plunger 2 of a plunger pump P is connected to a pneumatic piston 4 that moves a cylinder 3. As the pneumatic piston 4 reciprocates in response to air pressure a.sub.1 and b.sub.1 supplied from air supply ports 5 and 6, the plunger 2 also reciprocates in a cylinder 7 having a cylinder head. Thus, a suction stroke and a discharge stroke are repeated, so that a liquid sucked in from a suction opening d is pressurized in a pump chamber C and then discharged from a discharge opening e. To prevent the liquid, which is pressurized at a high level by the plunger 2 in the pump chamber C, from leaking to the air cylinder 3 through the outer peripheral surface of the plunger 2, a seal member 8 having a U-shaped cross section is provided on the inner periphery of the cylinder 7 to thereby seal the area between the cylinder 7 and the plunger 2, as shown in FIGS. 4 and 5. The seal member 8 is secured in a predetermined position by mounting members 9 and 10, which are provided on the inner periphery of the cylinder 7. The seal member 8 comes into pressing contact with the plunger 2 and the cylinder 7, particularly when the pressure in the pump chamber C is high, thereby preventing the liquid from leaking to the outside.
The conventional plunger pump, as shown in FIG. 4, suffers, however, from the problem that when the plunger 2 reciprocates in the cylinder 7 while in sliding contact with the seal member 8, minutes dust particles are generated by friction between the seal member 8 and the plunger 2 which causes these members to wear, and the resulting dust particles may enter the pump chamber C and comingle with the liquid to be delivered.
In particular, when the plunger pump is employed as a jet scrubber in semiconductor manufacturing equipment, minute dust particles mixed in the liquid are blown on a semiconductor substrate and attached thereto as foreign matter, which causes an adverse effect on the yield of semiconductor products made from the semiconductor substrate.
In addition, if, as shown in FIG. 5, such dust particles 11 gather on the liquid side (the side denoted by reference numeral 12) of the seal member 8, the dust 11 may wedge into the area between a lip 13 of the seal member 8 and the outer peripheral surface of the plunger 2, degrading the performance of the seal member 8. In addition, there is another problem in that the dust 11, which has gathered at the lip 13, may adhere to the surface of the plunger 2 and enter the pump chamber C during the discharge stroke, resulting in foreign matter being mixed in the liquid to be delivered.